Graphene is a one-atom-thick planar sheet of sp2-bonded carbon atoms that are densely packed in a honeycomb crystal lattice. The carbon-carbon bond length in graphene is about 0.142 nm. Graphene is the basic structural element of some carbon allotropes including graphite, carbon nanotubes and fullerenes.
Currently, large graphene “single crystal” films can be produced by mechanical exfoliation (repeated peeling) of graphite crystals. However, graphene produced by this method is of very limited size (e.g., at most a few hundred micrometers on the side), very expensive, not scalable, and very difficult and impractical to implement in an industrial environment.
Another method for producing graphene is to heat silicon carbide to high temperatures (e.g., much greater than 1,400° C.) to evolve silicon atoms preferentially from the silicon carbide surface to form a few layers of graphene. The layers of graphene in this case are crystallographically rotated with respect to each other such that the top layer behaves electrically as graphene rather than graphite. This process produces a sample size that is dependent upon the size of the silicon carbide substrate used. Furthermore, the quality of the graphene produced from this process degrades at the crystallographic step edges. The face of the silicon carbide used for graphene creation highly influences the thickness, mobility and carrier density of the graphene. One major disadvantage of the graphene synthesis on silicon carbide process is that even if it were scalable to large diameter crystals, it is not possible to use it for applications other than just on silicon carbide. There are many situations where graphene needs to be integrated with other applications, such as silicon integrated circuits, transparent conductive electrodes for displays or photovoltaic devices, membranes, etc.
Therefore, there is a need in the art for the synthesis of standalone graphene films with properties equivalent to exfoliated graphene from natural graphite that is scalable to size far greater than that available on silicon carbide, single crystal silicon substrates or from natural graphite.